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Indium is a very soft, silvery-white true metal that has a bright luster. As a pure metal indium emits a high-pitched "cry" when it is bent. Both gallium and indium are able to wetglass.

One unusual property of indium is that its most common isotope is very slightly radioactive; it very slowly decays by beta emission to tin over time. This radioactivity is not considered hazardous, mainly because its decay rate is nearly 50,000 times slower than that of natural thorium, with a half-life of 4.41×1014 years, four orders of magnitude larger than the age of the universe. Also, indium is not a notorious cumulative poison like its neighbor cadmium, and is relatively rare.

Indium's freezing point of 429.7485 K (156.5985 °C) is a defining fixed point on the international temperature scale ITS-90.

Indium's high neutron capture cross section for thermal neutrons makes it suitable for use in control rods for nuclear reactors, typically in an alloy containing 80% silver, 15% indium, and 5% cadmium.

In nuclear engineering, the (n,n') reactions of 113In and 115In are used to determine magnitudes of neutron fluxes.

111In is used in medical imaging to monitor the activity of white blood cells. A blood test is taken from the patient, white cells removed and labelled with the radioactive111In, then re-injected back into the patient. Gamma imaging will reveal any areas of high white cell activity such as an abscess.

Very small amounts used in aluminium alloy sacrificial anodes (for salt water applications) to prevent passivation of the aluminium.

Indium is produced mainly from residues generated during zincore processing but is also found in iron, lead, and copper ores. The amount of indium consumed is largely a function of worldwide LCD production. Increased manufacturing efficiency and recycling (especially in Japan) maintain a balance between demand and supply. The average indium price for 2005 was US$900 per kilogram. This is unusually high. Demand increased as the metal is used in LCDs and televisions, and supply decreased when a number of Chinesemining concerns stopped extracting indium from their zinc tailings. In 2002, the price was US$94/kg.

Up until 1924, there was only about a gram of isolated indium on the planet. The Earth is estimated to contain about 0.1 ppm of indium which means it is about as abundant as silver, although indium is in fact nearly three times more expensive by weight. Canada is a leading producer of indium. The Teck Cominco refinery in Trail, BC, is the largest single source, with production of 32,500 kg in 2005, 41,800 kg in 2004 and 36,100 kg in 2003. Worldwide production is typically over 300 tonnes per year, but demand has risen rapidly with the increased popularity of LCD computer monitors and televisions.

Pure indium in metal form is considered non-toxic by most sources. In the welding and semiconductor industries, where indium exposure is relatively high, there have been no reports of any toxic side-effects.

This may not be the case with indium compounds: there is some unconfirmed evidence that suggests that indium has a low level of toxicity. Other sources are more definite about indium compounds' toxicity - for example, the WebElements website states that "All indium compounds should be regarded as highly toxic. Indium compounds damage the heart, kidney, and liver, and may be teratogenic."[2] For example, indium trichloride anhydrous (InCl3) is quite toxic, while indium phosphide (InP) is both toxic and a suspected carcinogen.